H index (for a researcher or a journal) is defined as N number of publications cited a minimum of N number of times. Assume H-index of a journal is 50 which means that each of 50 articles of the journal is cited at least 50 times. H index can never exceed the total number of publications of a researcher or a journal. There is no formula or empirical relationship to compute H index. I have attached a sample H index graph from a Scopus profile (https://www.scopus.com/authid/detail.uri?authorId=37123770900). This researcher has 87 documents in his Scopus profile. The citations per document are plotted in descending order. His H index is 21 which means at least 21 articles are cited 21 times or more as seen in the graph. Alternatively, H index is the unit length of the side of the biggest square that can be drawn in the area under the graph.The diagonal of such as square will have end points as (0,0) and (21,21). His H index will move to 22 if all the previous 21 articles receive at least 22 citations each and one more article reaches 22 citations.

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Most welcome Karima Khalil and Temitayo O. Olaniyan

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An interesting issue. The h-index citation index is one of the key indicators of the level of citation of scientific publications and can be a component of the assessment of the scientific achievements of a particular researcher and researcher. Many scientists ask about this issue on the Research Gate website, indicating that h-index is included and plays a key role in the biographical note of the author of scientific publications collected, archived in specific database systems of scientific knowledge and indexes of scientific publications. However, not on all of these scientific knowledge databases, this indicator is given at the author's biographical note. The principles of including this indicator in models for assessing scientific achievements and in determining the relation of the h-index relative to other similar measures of the archived scientific system should be globally standardized.

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The h-index is an author-level metric that attempts to measure both the productivity and citation impact of the publications of a scientist or scholar. The index is based on the set of the scientist's most cited papers and the number of citations that they have received in other publications. The index can also be applied to the productivity and impact of a scholarly journal as well as a group of scientists, such as a department or university or country.The index was suggested in 2005 by Jorge E. Hirsch, a physicist at UC San Diego, as a tool for determining theoretical physicists' relative quality and is sometimes called the Hirsch index or Hirsch number.

Formally, if f is the function that corresponds to the number of citations for each publication, we compute the h-index as follows. First we order the values of f from the largest to the lowest value. Then, we look for the last position in which f is greater than or equal to the position (we call h this position). For example, if we have a researcher with 5 publications A, B, C, D, and E with 10, 8, 5, 4, and 3 citations, respectively, the h-index is equal to 4 because the 4th publication has 4 citations and the 5th has only 3. In contrast, if the same publications have 25, 8, 5, 3, and 3 citations, then the index is 3 because the fourth paper has only 3 citations.

f(A)=10, f(B)=8, f(C)=5, f(D)=4, f(E)=3　→ h-index=4

f(A)=25, f(B)=8, f(C)=5, f(D)=3, f(E)=3　→ h-index=3

If we have the function f ordered in decreasing order from the largest value to the lowest one.